The present invention generally relates to a dielectric coaxial resonator including a cylindrical dielectric member and more particularly, to a resonator device equipped with the dielectric coaxial resonator and a mounting member having the dielectric coaxial resonator secured thereto.
Conventionally, in dielectric coaxial resonators, it has been, for example, so arranged as shown in FIG. 1 that a 1/4 wavelength TEM-mode (transverse electro-magnetic mode) coaxial resonator 1 generally includes an inner conductor 2, an outer conductor 3 and a cylindrical dielectric member 4 made of, for example, ceramic dielectric material of titanium oxide group such that the dielectric member 4 is disposed between the inner conductor 2 and the outer conductor 3. More specifically, the dielectric member 4 is formed with a central bore so as to be of annular shape having a large wall thickness. The inner conductor 2 and the outer conductor 3 are, respectively, formed on inner and outer cylindrical surfaces of the dielectric member 4 by baking thereonto a material, e.g. silver paste, having superior high frequency electrical conductivity and also an excellent property of closely adhering to the dielectric member 4. The resonator 1 has an electrically open end 7 and a short-circuiting end 10 which are, respectively, disposed at opposite ends of the dielectric member 4. Meanwhile, the inner conductor 2 has a bore formed therein and a central rod 5 made of, for example, ceramic material and having a length larger than that of the dielectric member 4 is fitted, for securing thereof, into the bore of the inner conductor 2 such that an end portion 6 of the central rod 5 projects out of the electrically open end 7 of the resonator 1. Furthermore, an electrode film 8 extending from the inner conductor 2 is coated on the end portion 6, while an electrode 9 for short-circuiting the inner conductor 2 and the outer conductor 3 is provided on the short-circuiting end 10 of the resonator 1.
Referring to FIG. 2, there is shown another prior art resonator 11 which does not employ the central rod 5 of the resonator 1. The resonator 11 includes a terminal electrode 12 of arbitrary shape and chip type capacitors 21 and 22. The terminal electrode 12 is fitted into the bore defined by the inner conductor 2 so as to be secured thereto by electrically conductive adhesive such that the terminal electrode 12 is electrically connected to the inner conductor 2. Meanwhile, the chip type capacitors 21 and 22 are used for capacitive coupling of the resonator 11 with other components such as other resonators, connectors, etc. Namely, one end of the terminal electrode 12 is formed into a proper shape so as to be electrically connected to one electrode 23 of the capacitor 21 and one electrode 24 of the capacitor 22. Meanwhile, one end of the lead wire 27 is connected to the other electrode 25 of the capacitor 21 and one end of a lead wire 28 is connected to the other electrode 26 of the capacitor 22 such that the other end of the lead wire 27 and the other end of the lead wire 28 are connected to other resonators, connectors, etc.
Referring to FIG. 3, there is shown a prior art electrical filter 30 employing a plurality of the resonators 11 of FIG. 2. The electrical filter 30 includes a first casing portion 40 having a shape of rectangular parallelopiped. The first casing portion 40 is made of electrically conductive material, for example, duralumin and has grooves 51, 52, 53 and 54 of semicircular cross section formed therein, in this order from one end of the first casing portion 40 to the other end of the first casing portion 40, in spaced and parallel relation to each other at intervals of a predetermined distance. Meanwhile, slots 61, 62 and 63 of semicircular cross section are, respectively, formed between the grooves 51 and 52, between the grooves 52 and 53 and between the grooves 53 and 54. Furthermore, slots 71 and 72 are, respectively, formed between the one end of the first casing portion 40 and the groove 51 and between the groove 54 and the other end of the first casing portion 40. It is to be noted here that the slots 71, 61, 62, 63 and 72 are formed in alignment with each other in this order from the one end of the first casing portion 40 to the other end of the first casing portion 40.
The electrical filter 30 further includes a second casing portion 41 of the same construction as that of the first casing portion 40. Namely, as shown in FIG. 4, a rectangular casing of the electrical filter 30 is of a two-piece construction constituted by the first casing portion 40 and the second casing portion 41. A half of the resonator 11 is fitted into each of the grooves 51, 52, 53 and 54 of the first casing portion 40 and the outer conductor 3 of the resonator 11 is secured to the first casing portion 40 by electrically conductive adhesive or screws so as to be electrically connected to the first casing portion 40. An input coaxial connector 81 and an output coaxial connector 82, whose half portions are, respectively, fitted into the slots 71 and 72, are fixed to the first and second casing portions 40 and 41 by a known method. A central terminal of the input coaxial connector 81 is connected, through a lead wire 91, to the capacitor 21 of the resonator 11 disposed in the groove 51. The capacitor 22 of the resonator 11 disposed in the groove 51 is connected, via a lead wire 92 extending through the slot 61, to the capacitor 21 of the resonator 11 disposed in the groove 52. Then, the capacitor 22 of the resonator 11 disposed in the groove 52 is connected, by way of a lead wire 93 extending through the slot 62, to the capacitor 21 of the resonator 11 disposed in the groove 53. Furthermore, the capacitor 22 of the resonator 11 disposed in the groove 53 is connected, via a lead wire 94 extending through the slot 63, to the capacitor 21 of the resonator 11 disposed in the groove 54. Moreover, the capacitor 22 of the resonator 11 disposed in the groove 54 is connected, through a lead wire 95, to a central terminal of the output coaxial connector 82.
As is clear from the above described construction of the electrical filter 30, it has been so arranged that the resonator 11 is secured to the first and second casing portions 40 and 41 by bonding thereto the outer conductor 3 by the use of electrically conductive adhesive 100 as shown in FIG. 5 or by inserting a copper net 110 impregnated with adhesive between the outer conductor 3 and the first and second casing portions 40 and 41 as shown in FIG. 6.
However, the known electrical filter 30 including the resonators 11 secured to the first and second casing portions 40 and 41 as described above has such a disadvantage that, since a linear expansion coefficient of the resonator 11 is vastly different from that of the first and second casing portions 40 and 41 or that of the adhesive, the outer conductors 3 of the resonators 11 are readily separated from the resonators 11 when the known electrical filter 30 is subjected to sharp change in temperature.
Furthermore, the known electrical filter 30 has such inconveniences that operations for securing the resonators 11 to the first and second casings 40 and 41 are troublesome and a long time period is required for curing the adhesive, thus resulting in an increased production cost.